The stethoscope was invented in France in 1816 by René Laennec for the purpose of auscultation, i.e., listening for sounds produced within the body mainly to assess the condition of organs and vessels including the heart, lungs, aorta, and intestines. Fetal heart tones can also be monitored during pregnancy by auscultation with specialized stethoscopes. Blood flow in blood vessels can also be auscultated. Auscultation performed with the unaided ear is called immediate or direct auscultation, and when a stethoscope is used it is called mediate auscultation.
The electronic stethoscope is the updated version Laennec's concept where a skin-contact diaphragm creates an acoustic chamber in which airborne sounds are converted to electrical signals. These signals are amplified, filtered or otherwise processed, and played through, e.g., a loudspeaker or earpiece. A significant amount of bodily sound information is in the frequency band 0.001 Hz to 100 Hz, and because the threshold of audibility rises sharply below 100 Hz, the amplification of the electrical signals to make them audible becomes difficult if not futile. Few current systems, even electronic stethoscope systems, have been designed for accurate and effective amplification within this range.